Polyphenylene ether resins have been modified with polyamide resins to provide a wide variety of beneficial properties such as excellent heat resistance, chemical resistance, impact strength, hydrolytic stability and dimensional stability compared to either unmodified resin alone.
The improved properties of polyphenylene ether-polyamide compositions have found great utility in thermoplastic applications which take advantage of such properties. Exterior automotive applications such as body panels and wheel covers all benefit from the improved thermal properties of polyphenylene ether-polyamide compositions (PPE/PA compositions). In an automotive application such as a fender part, a satisfactory thermoplastic must be processed at elevated extrusion and molding temperatures. Such parts also experience high temperature finishing processes such as oven baking for paint and other finishes.
Many important thermoplastic applications for PPE/PA compositions also require that the resin be impact modified to provide adequate performance. Impact modification of plastics by incorporation of rubber-like modifiers offers many advantages and disadvantages. Conventional impact modifiers for PPE/PA compositions are either costly or ineffective compared to the impact modification system of the present invention.
Conventional unsaturated impact modifiers such as SBS rubber (styrene-butadiene-styrene copolymer) have shown deficiencies in PPE/PA compositions requiring thermal stability. A rapid drop in impact strength of PPE/PA compositions after high temperature molding conditions over a prolonged period has been attributed to the use of unsaturated rubber impact modifiers.
It has now been discovered that PPE/PA compositions can be improved by combining the base resin with an impact modifier comprised of crosslinked acrylate core/crosslinked styrenic shell in accordance with the description below. In contrast to conventional PPE/PA compositions, those of the present invention have improved melt stability and heat aging characteristics.